Tom Steyer uses a blue ballpoint pen to draw the sign of the cross on his left hand every day. He drives an old Honda hybrid, wears wool plaid ties and prefers camping to the Four Seasons. As he says, "One of the things that's true in this world is you can really only eat three meals a day and wear one pair of pants and shirt at a time."

His wife, Kathryn "Kat" Taylor, loves spending long days running a small bank in a gritty part of Oakland. She is pragmatic, has an unfettered laugh and sports six tattoos, admitting, "There's no doubt if I turned up for a black tie event at the Pacific Union Club, I might not be what people expect to see."

Steyer and Taylor - he a hedge fund billionaire turned heavy-hitter Democratic donor - live in San Francisco's outer Pacific Heights. They are one of the city's great philanthropic couples, but eschew the social scene in favor of pushing for social change, whether it's for a better environment or helping the disadvantaged.

Steyer stepped away Jan. 1 from Farallon Capital, the investment firm he founded in 1986, to devote all of his time, energy and resources to working on reversing global warming. Taylor is on a mission to use One PacificCoast Bank, which she and Steyer opened in 2007, to help those typically shunned by mainstream financial institutions.

"Tom and Kat are very clear-headed about what they want to achieve, and anything that is extra is not necessary," said Michael Kieschnick, president of CREDO Mobile, a company that uses its revenue to support progressive philanthropy and activism. He has known Steyer and Taylor since the 1980s.

"I have the privilege of knowing both of them pretty well," added Kieschnick, who is on the board of the foundation that owns One PacificCoast Bank. "Tom feels a sense of urgency about global warming and he's right, and Kat believes in taking in deposits from like-minded people and recycling them into a community to lift people up and achieve social goals."

Their social goals

Steyer, 55, earnest and emphatic, said, "I believe global warming is the big moral issue of our time. I want to change the dialogue and practices around energy." And Taylor, 54, said, "I am holding the torch for this mission every minute of every day. I think we have an opportunity to create a society, an economy, a world, where things happen right and you don't have to come in and correct the injustices."

Steyer was born and reared in New York City, the youngest of three boys. His father, Roy, was a Yale graduate and litigator at Sullivan & Cromwell, the white-shoe law firm in New York. His mother, Marnie, wrote and produced for the NBC evening news and later established reading programs in public schools and taught in Harlem.

Sitting in a conference room at Farallon Capital in late December - the day before he would leave the firm that started with $8 million in capital and grew to a powerhouse with about $20 billion in assets - Steyer said, "I really admire my mother's courage and openheartedness. She had a willingness to stick up for the underdog. And my father was always kind and respectful to other people."

In Steyer's family, education came first, and doing a good job was more important than having a good job. Steyer attended elite private schools, including the Buckley School, Phillips Exeter Academy and Yale, where he graduated summa cum laude and was captain of the university's soccer team. He earned his master's degree in business from Stanford.

Taylor, whose father is an electrical engineer and whose grandfather was the president and chairman of the Crocker National Bank, grew up in San Mateo. She attended Crystal Springs Uplands School in Hillsborough before graduating from Harvard and earning a four-year doctor of law and master of business administration from Stanford.

'No lollygagging'

"In our family, we were either working or going to school," Taylor said, sitting in One PacificCoast Bank in downtown Oakland. "There was no lollygagging around."

Steyer and Taylor met on the track at Stanford. Taylor had been the captain of her college track team, and was training for a marathon by doing sprints with two guys. Steyer, who had been trying to meet Taylor - a mutual friend thought they would hit it off - spotted her on the track and asked whether he could join in the workout.

"We were doing these repeat miles, where you do a 5:45-minute mile and then you take a two-minute rest," Taylor recalled of their workout, timed to the second to improve conditioning. "Tom walked over at mile 4, and I think he had these low-top Converse flat shoes on and said, 'Can I run with you?' I was like, 'Fine. Whatever.' So he's running with us and starting to chat. Just making friendly conversation. I was like, 'I'm not talking in the middle of the mile.' Then he took off and blew the time - he ran it in 5:30 - and I thought, 'Ohhhh, this aggravating man!' "

Laughing, she added, "I guess I was neurotic about track and a little thick about romance." The two ended up training for a marathon together, and were married on the Stanford campus in August 1986. They went camping on their honeymoon.

Steyer, who had worked in the risk arbitrage department at Goldman Sachs in New York, started Farallon in January 1986 with seed money from San Francisco investment bankers Warren Hellman and Tully Friedman.

"I always loved investing," Steyer said. "When I was 17, New York almost went bust and needed a bailout. There was a four-story townhouse in our building going for $40,000. I told my dad we should buy it while it was cheap. But my mother and father were not into investing. They put their money into a bank, where it was 'safe.' They would say, 'We're not going broke. We're not getting rich.' "

Steyer and 1 assistant

Farallon began with Steyer and one assistant working in a tiny office on Bush Street in the Financial District. Steyer started by buying penny stocks and looking for "special situations," such as buying up distressed debt. Soon, Farallon was investing primarily for endowments and foundations, including his alma mater, Yale. Over the years, returns averaged 15 percent.

"I loved it, and I did it for 27 years," Steyer said. "Before I started, I told Kathryn, 'No one does this for more than 10 years. It's too much stress.' "

Taylor, meanwhile, went from four years of Stanford business school straight into a nine-month credit-training program at Wells Fargo.

Before starting there, she sought job advice from Stanford alumnus Kieschnick, recommended to her by a mutual friend. Kieschnick had been head of economic development in Gov. Jerry Brown's first administration, and co-founded Working Assets, a wireless services and credit card company that supports nonprofit and environmental organizations.

"I went to him, nervous as all get-out, and he looked at my resume and saw I had worked summers at my grandfather's bank," Taylor recalled. "Michael said to me, 'You should think of starting a beneficial bank.' I thought, 'Are you frickin' out of your mind? I'm 28. Have no capital. Tom and I have two sticks to rub together.' "

Kieschnick was undeterred, telling Taylor: "Learn the ropes, and get ready to start a bank" that will help an economically distressed community.

Taylor finished the training program at Wells Fargo and applied to work in the middle market lending department. "The hot departments were real estate and corporate finance," she recalled. "I applied to the more humdrum area, which was lending to businesses doing $100 million or less. It suited me."

Within two years at Wells Fargo, though, Taylor became pregnant with their first child, Sam, who is now 24. Sam was followed by Gus, 23, Evi, 21, and Henry, 19. Sam, who graduated from Harvard, now works for a nonprofit bringing technology to rural Tanzania (for Christmas vacation, the whole family hiked Mount Kilimanjaro); Gus and Evi are at Yale; and Henry will attend Harvard after taking a gap year.

"I stayed home to raise the kids and didn't make money for nearly 20 years, but sat on a ton of boards and loved it," Taylor said of her work with the Good Samaritan Family Resource Center for new immigrants and the Insight Prison Project, focused on restorative justice.

By 2004, with the kids more independent, Taylor began to think about returning to work. Steyer was a major backer of John Kerry in his bid for president that year, and was considered a shoo-in for a position in Kerry's administration.

"When he lost, we thought, 'What do we do now?' " Taylor said. "Then we said, 'Maybe we should start that bank!' " By this time, Steyer had amassed a stellar reputation - and considerable fortune - on Wall Street West. The two met with friends in finance and began to study banks with a social purpose.

They found an inspirational model in the microfinance and community development Grameen Bank started by Muhammad Yunus in Bangladesh. They also looked at the ShoreBank in Chicago, which was started in the 1970s to undo the pernicious affects of redlining, where banks didn't lend in poorer neighborhoods in Chicago's South Side.

Today, One PacificCoast Bank is one of 60 CDFI-certified (Community Development Financial Institution) banks in America, a sought-after designation given by the U.S. Treasury. The national program, started in 1994, gives grants to community banks that increase lending and investment in poor and low-income neighborhoods.

"I'm an unconventional CEO to be sure," Taylor said, laughing. "I work for two years and step away for 20. But, my belief, and this is something I think about every day, is that we don't just want to be another bank. We need to achieve measurable outcomes in social justice and environmental well-being."

As Taylor spent more and more time at the bank, Steyer - a major supporter of Barack Obama - found an outlet for his activism through ballot measures. In 2010, he joined forces with former Secretary of State George Shultz in fighting Proposition 23, which would have suspended California's landmark climate change law. In 2012, he put $30 million of his own money into Proposition 39, which was approved by voters and closed a tax loophole championed by Republicans to benefit out-of-state corporations. It will send an additional $1 billion a year to the state.

Investment pays off big

"If I can spend $30 million of my money and get a billion for the state every year, that's exciting," Steyer said. He and Taylor gave more than $40 million to create the TomKat Center for Sustainable Energy at Stanford, focusing on the development of more affordable renewable energy and the advancement of public policies around renewable energy. And last weekend, Steyer, looking very much like a politician in the making, gave a rousing speech at the huge climate change rally in San Francisco, saying, "The time for business as usual has passed. We can't afford 40 more years of dirty energy. We need to build a cleaner, cheaper, more secure energy system."

Sitting back in his chair, Steyer, who is studying the energy problem as he decides where he can have the most impact, went on, "I have this theory: As you get older you start to realize the things you really truly care about. Worrying about materialism is kind of crazy. When Kat and I were married, we had a plan to send our kids to good schools and have enough money for health care when we got old. We focused on good investing, not on making money. What I care about today is trying to be a good person."

'I am striving'

Steyer said the image of the cross on his hand is his reminder of what's important.

"I didn't spend a lot of time on religion until I was 40 and had my midlife crisis," Steyer said. "I now go to Grace Cathedral every Sunday. I sit in the back. It's a place where you can find meaning. It makes you think about your responsibilities to one another and to the planet."

Two years ago, Steyer and Taylor signed on to the Giving Pledge, the philanthropic endeavor spearheaded by Warren Buffett and Bill Gates, in which America's wealthiest individuals and families agree to give the majority of their wealth to philanthropic causes.

In their pledge letter, Steyer wrote of living in San Francisco, a "city named for a man who stripped himself of worldly goods." He wrote, "Surely the pleasure we derive from St. Francis' active verbs of consoling, understanding, loving, giving and pardoning far outweigh any selfish and passive pleasures of owning, having, or possessing."

Steyer and Taylor ended the letter with, "We relish the opportunity to do our part and leave our collective campsite cleaner and better tended than we found it. It's our pleasure at least as much as our obligation. We hope St. Francis approves."